In the day of the performance I like to feel very well. So I get off my schedule anything annoying, have a fantastic breakfast and lunch (if the concert isn't at noon), walk around, listen to some music.
I try to arrive at the theater at least one hour before the apointment, to feel the place, its acoustics. Then, a moment before as you said, I need to take some time feeling my muscles and my breath.
Maybe the most important: I never play a single note or think of any part of the repertory before the recital.
Finally, I always start with something very quite, easy and smooth to feel public's and hall's feedback.
Of course, at times everything goes wrong cause anything else seems to conspire against, and you only notice that have to play when you sit at the piano and notice that the spot is on you. However, sometimes these are the best days...